The disclosed subject matter relates generally to anodized aluminum coatings, and more specifically to sealing and protecting anodized aluminum coatings.
Anodized aluminum coatings, used in a number of industries and applications, have a very thin barrier layer under a more porous main coating structure. To improve corrosion resistance of the coating and substrate, anodized aluminum coatings are often sealed. Conventionally, hexavalent chromium (Hex-Cr) compounds have been used to seal anodized aluminum coatings and improve corrosion resistance. However, Hex-Cr sealants are toxic and carcinogenic and thus are being phased out in favor of more environmentally- and health-friendly compounds.
One common substitute for Hex-Cr includes variants on trivalent chrome process (TCP) sealing. Effective sealing, particularly for TCP sealants requires deep sealant penetration and homogeneous distribution within the anodized coating. A panel with a commercially available trivalent sealing technology can provide reasonable sealing which often can pass the minimum 336 hr neutral salt fog chamber (ASTM B117) test requirement. However, the process still needs to be controlled very strictly according to published procedures to provide suitable opportunity for sealing and yet, the results are often mixed for very thin anodized coatings (<500 mg/ft2). Among other factors, shortening the processing time reduces penetration and effectiveness for each conventional TCP sealing technology.